Due to regulatory demands, it is necessary to check the weight of a blister once it has been filled with powdered medicament. The process of producing a dose of medicament must be tightly controlled such that each dose is accurate and consistent; otherwise, a patient's health is put at risk.
Accurate dosing of powdered medicament into blisters is difficult and can be exacerbated by the flow properties of the active pharmaceutical ingredient (API). A batch of filled blisters containing poorly controlled quantities of medicament can, depending on the API, be an expensive waste. Therefore, quickly establishing whether the filling line is performing as required is crucial.
Devices for weighing products following manufacture are known generally in the art as checkweighers. An in-line checkweigher requires each product to be weighed to pass over a balance facility whilst travelling along a transport device, such as a conveyor belt. When the products are spaced apart, current checkweighers are fast enough to weigh each product passing over the balance. However, the problem with the production of pharmaceutical blisters is the sheer quantity produced at high speed. Presently, it is impossible to accurately weigh individual blisters in-line without significantly reducing the line speed, which would seriously compromise production costs.
Furthermore, the in-line weighing of a sample of blisters in a batch has been found to be error prone since it requires the complete removal of all powder within the blister, which cannot be assured at higher speeds.
As such, a number of off-line weighing operations have been developed specifically for medicament filled blisters. One option is to determine individual blister fill weights by manually weighing each blister in a batch and subtracting the mean packaging weight. Alternatively, individual blister fill weights can be measured by evacuating the blister and subtracting the weight of the powder from the specific packaging weight for that blister.
However, in practice these processes have been found to be time consuming, awkward and lacking good reproducibility.
Moreover, in the case of blister strips, it is not possible to establish the individual blister fill weights because the blister strip packaging remains connected. The weight of the blister strip packaging far exceeds the weight of the powder contents, making a mean packaging weight determination impractical and unreliable.
In view of the problems outlined above, the present invention seeks to provide a fast and reliable offline process for accurately determining the weight of powdered medicament in a filled blister unit or blister strip.